I'm 20 and my gums are receding. What should I do? How bad is it really? (Photo)

Hi there, and thanks for your question.
Although you do seem to be showing signs of receding gums, the good news is
that you appear to have caught it early. The first step to alleviating the
issue is determining its cause. Gum recession can have many different causes,
ranging from brushing your teeth too aggressively to certain medical
conditions. I recommend seeing your regular dentist or a periodontist to learn
what's causing your receding gums. Once you understand the cause, you can work
together to find the solution.

First of all, bare minimum, you want to see your dentist to monitor the recession.  However, at your age I would suggest that you take action before the situation worsens.  Whether the recession is caused by extreme brushing, localized bone loss, malocclusion (teeth hitting incorrectly), the ligament/frenum pulling on the gums or unattached gum tissue, it is imporant to figure out the cause so you can discover the best treatment option.  I would recommend evaluation by a periodontist (bone and gum specialist) and look into fixing the cause and work towards how to repair.  Most likely you will require a gingival graft to replace the lost and receeding tissue.